This proposal will extend our observation that onion and garlic oils inhibit the promotion of mouse skin tumorigenesis. The major goal is to identify the active components of these oils. Onion and garlic oils are composed of aliphatic di- and tri-sulfides which can be obtained commercially or by synthesis. These components will be tested for their ability to inhibit promotion. The active components will be tested for their ability to inhibit initiation, first and second stage promotion, tumorigenesis by a complete skin carcinogen, and tumorigenesis in internal organs. The mode of action of the active components will be determined by correlations with inhibition of lipoxygenase, cyclooxygenase, ornithine decarboxylase, and superoxide release. Extracts of fresh onions, prepared at room temperature and by boiling, will be examined for the presence of the active components. Extracts of other members of the Allium family will also be examined for these components. The effects of feeding protease inhibitors, isolated from soybeans, and a copper chelate with superoxide dismutase properties, to mice with dimethylhydrazine-induced colon cancer will also be determined. The identification of non-toxic constituents of natural foodstuffs that inhibit tumorigenesis would contribute to our comprehension of the role of nutrition in human cancer and lead to dietary recommendations that would be beneficial in cancer prevention.